A persistent problem common to virtually all petroleum products and petroleum-related products is their tendency to undergo oxidative degradation. Oxidation may occur even under the relatively mild conditions attending storage and transport of, e.g., fuel oils, and is appreciably accelerated when operating conditions are conducive to oxidative processes, for example the elevated temperatures experienced by lubricating oils. Such oxidative processes not only cause chemical degradation of the petroleum or petroleum-related product, but may also cause appreciable changes in desirable physical properties, such as viscosity, which lead to a deterioration in performance of the product. Additionally, the oxidative products themselves may attack materials in contact with petroleum and petroleum-related products, such as metals in contact with transmission or lubricating oils, thereby inducing inefficient performance and, in some cases, even structural failure.
It has been known for some time that certain hydroxy aromatic compounds are effective antioxidants useful in a wide range of applications. For example, the food additive commonly known as BHA is 2-t-butyl-4-methoxyphenol. Other phenols have been utilized as antioxidants in petroleum products, in plastics, in lubricants, and in other applications where increased oxidative stability is desired. Certain polyalkylated hydroxy-substituted aromatics are especially effective antioxidants. Thus, 2,4-di-t-butylphenol is of commercial utility as an antioxidant and stabilizer when added to fuel oils. However, because of their physical properties the use of hydroxy aromatic compounds as antioxidants in the past has been limited to relatively low temperature applications.
It now has been found that alkylated 5,6,7,8-tetrahydronaphthalenols exhibit antioxidant properties over a wide temperature range and possess the necessary chemical and physical properties to permit their use in higher temperature applications, such as transmission oils, as well as lower temperature application as, for example, in storage of fuel oils.